优先队列（priority queue）
优先队列中，元素（item）按键值（key value）排序，键值最低的元素位于队首，键值最高的元素位于队尾；反之亦然。
基本操作
-
插入（insert、enqueue）
-
删除（remove、dequeue）
实现
class PriorityQuery(object):
"""
priority query with higher the value, higher the priority
queue order - high priority (front) -> low priority (rear)
"""
def __init__(self, max_length):
self._queue = []
self._max_length = max_length
def __str__(self):
return " ".join([str(item) for item in self._queue])
def is_empty(self):
return len(self._queue) == 0
def is_full(self):
return len(self._queue) == self._max_length
def insert(self, item):
"""
insert an item into the queue
"""
# the queue is empty
if self.is_empty():
self._queue.append(item)
return 0, item
# if the queue is not empty, traverse the queue to find the position
# where the item is inserted
for idx in range(len(self._queue)):
# the position new item will be inserted
if self._queue[idx] <= item:
self._queue.insert(idx, item)
# if the queue has been full before insertion
if len(self._queue) > self._max_length:
self._queue.pop()
return idx, item
# the queue is not full and the item has the lowest priority
if not self.is_full():
self._queue.append(item)
return len(self._queue) - 1, item
def delete(self):
"""
pop the item with the lowest priority,
i.e. the last item in the queue
"""
if not self.is_empty():
return self._queue.pop()
测试：
queue = PriorityQuery(max_length=10)
for item in [1, 1, 2, 3, 4, 5, 12, 23, 34, 12, 32, 1, 35, 43, 4, 19, 100]:
result = queue.insert(item)
if result:
print("insert {0[1]} at position {0[0]}".format(result))
print("now, the queue is:", queue)
insert 1 at position 0
now, the queue is: 1
insert 1 at position 0
now, the queue is: 1 1
insert 2 at position 0
now, the queue is: 2 1 1
insert 3 at position 0
now, the queue is: 3 2 1 1
insert 4 at position 0
now, the queue is: 4 3 2 1 1
insert 5 at position 0
now, the queue is: 5 4 3 2 1 1
insert 12 at position 0
now, the queue is: 12 5 4 3 2 1 1
insert 23 at position 0
now, the queue is: 23 12 5 4 3 2 1 1
insert 34 at position 0
now, the queue is: 34 23 12 5 4 3 2 1 1
insert 12 at position 2
now, the queue is: 34 23 12 12 5 4 3 2 1 1
insert 32 at position 1
now, the queue is: 34 32 23 12 12 5 4 3 2 1
insert 1 at position 9
now, the queue is: 34 32 23 12 12 5 4 3 2 1
insert 35 at position 0
now, the queue is: 35 34 32 23 12 12 5 4 3 2
insert 43 at position 0
now, the queue is: 43 35 34 32 23 12 12 5 4 3
insert 4 at position 8
now, the queue is: 43 35 34 32 23 12 12 5 4 4
insert 19 at position 5
now, the queue is: 43 35 34 32 23 19 12 12 5 4
insert 100 at position 0
now, the queue is: 100 43 35 34 32 23 19 12 12 5
